This invention relates generally to mist generating systems for atomizing liquids, such as for generating an oil mist for lubricating machine parts, and more particularly concerns a mist generating head for the same.
The physical structure in which mist generation occurs is referred to as a mist generating head. Means for pneumatic atomization of a liquid for generating a mist typically comprise nozzles fitting in the head and having an integral venturi or vortex chamber. Pressurized or compressed gas flows through the mist generating nozzle at near acoustic velocity. A reduced pressure region is created in the mist generating head drawing liquid into the nozzle from a liquid supply source. Gas and liquid are combined in the nozzle. The action of the turbulent stream of pressurized gas subjects the liquid to a condition of high stress, breaking down the liquid into extremely small and substantially uniform mist particles suspended in the gas stream. Larger particles fall out of the gas stream, leaving the smaller ones to remain air borne. A baffle is typically placed downstream of the nozzle outlet. The heaviest of the air borne liquid particles strike the baffle and fall out. The smaller mist particles can change direction and avoid the baffle. The gas stream transports the tiny liquid particles constituting the mist through a header system and delivers the particles to points of use.
Centralized mist generating systems are used to provide an oil mist for continuous lubrication of multiple pieces of equipment. Oil mist lubricating systems generally include a pressurized inlet gas supply, an inlet oil supply feeding into an oil reservoir, a mist generating head and instrumentation for monitoring and controlling the operating variables of the system. Using the energy of pressurized gas, oil is atomized into very fine particles at a central location. The oil mist is conveyed long distances in the gas stream and directed to machinery parts for lubrication. Oil mist lubrication is used to lubricate all kinds of machine elements ranging from tiny, ultra-high speed parts of dental drills to huge chains, cams, gears, bearings and other moving machine parts.
The heart of any oil mist lubricating system is the mist generating head. A basic mist generating head consists of a pressurized gas inlet, an oil inlet and a mist generating nozzle. However, oil mist generating heads are quite limited in the functions they perform. Present mist generating heads are typically designed based on the system capacity. Small oil mist generators do not use the same mist generating head as large generators. While nozzles having different mist generating capacities may be interchanged in a head, only slightly different amounts of oil mist can be generated by the head. High volume mist generating nozzles simply do not fit small mist generating heads.
Another problem with oil mist generating systems is the large number of component parts. Certain components of the oil mist lubricating system may be unitary with the mist head, such as an air pressure regulator, an inlet air pressure gauge or an oil reservoir filling port. However, oil heaters, float switches, associated instrumentation, etc., still remain as separate components. An operator of many different sizes of oil mist systems in a large facility is required to keep a large number of replacement parts on hand for service and maintenance of each of the systems.
From the standpoint of the oil mist lubricating system manufacturer, this problem is multiplied when an oil mist product line includes several different size systems. Many inventory items are required to maintain a product line and purchasing must be done on an as-needed basis in small quantities. Designing and manufacturing custom parts to meet a customer's changing needs cannot be accomplished without extraordinary efforts and costs, and is economically impractical.
Present oil mist lubricating systems are also difficult to service. Malfunctions often require shutting down the lubricating system and, in the absence of a redundant unit, the lubricated equipment. There are numerous parts which must be removed or disconnected. Problem diagnosis and repair further extends downtime. Since both the tank and head are rigidly mounted, even the simple task of cleaning an oil pickup screen inside the reservoir requires that various lines be disconnected and multiple head screws removed to access the screen. Productivity is sacrificed due to the time and labor involved in maintenance and repair.
Another problem with conventional oil mist lubrication systems is, once in place, there are few changes that can be made to a system. If the user wants to modify an existing system, such as change the tank size or increase system capacity for instance, there is little that can be done to adapt the system accordingly. Therefore, if the user's lubrication needs increase or decrease the only choice is to purchase and install a new system at significant additional expense.
For the foregoing reasons, there is a need for a mist generating head adapted for a wide range of sizes of mist generating systems. The mist generating head must be interchangeable with small and large mist generators. Ideally, the mist generating head components should also be fully interchangeable regardless of the mist generator capacity. The mist generating head should allow for more flexibility in configuring and adapting the system to the user's requirements. The new mist generating head needs to allow for an upgrade without completely upfitting or scrapping an existing unit. Further, the mist generating head should be easy to maintain and enable service to the system with a minimum of downtime. At the same time, the mist generating head needs to be straightforward and inexpensive to manufacture, and require a minimum of parts to produce and maintain.